Chinese Utility Model Patent No. CN2038980u discloses a diaphragm shutoff valve. The valve comprises a valve body with a valve seat, a valve cap fixed hermetically to the valve body, a diaphragm and a valve core located in the valve chamber defined by the valve body and the valve cap. The diaphragm edge is between the valve body and the valve cap and the diaphragm is disposed to the valve core. There is a vertical chamber in the valve body and the valve cap, which has three openings that are connected to the outlet and inlet passage of the valve body and the fluid chamber defined by the diaphragm and the valve cap. A valve rod together with a set of valve clacks are provided in the vertical chamber, which constitutes a small manual control valve. When the valve rod is rotated clockwise, the clacks will block the outlet of the valve body and open the inlet of the valve body at the same time, by which the pressure fluid coming from the inlet passage of the valve body enters into the liquid chamber through vertical chamber, pushes the diaphragm and valve core downwards and then against the valve seat, and as a result, the shutoff valve is shut. When the rod is rotated anti-clockwise, the clacks will block the opening connected to the inlet of the valve body and open the opening connected to the outlet of the valve body at the same time, by which the pressure fluid flows out of the liquid chamber through vertical chamber into the inlet fluid passage of valve body, pushes the valve core and diaphragm away from valve seat, and as a result, the shutoff valve is opened.
The above-mentioned shutoff valve is controlled by a small control valve working under the force of the pressure fluid, which make it convenient to open or shut the valve. But the shutoff valve also has some defects resulting from its structure.